1. Technical Field of the Invention
The present invention relates to a body frame damping structure in a saddle-type vehicle disposed with a damping force generating means that is disposed so as to bridge portions of the body frame with other portions of the body frame. With the damping force generating means being respectively coupled, the portions and the other portions are elastically deformed when an impact force is applied to the body frame by the road surface.
2. Prior Art
Conventionally, there are saddle-type vehicles. A vehicle is disposed with a body frame configuring a frame of the vehicle body, a front fork steerably supported at a front end portion of the body frame, a front wheel supported at lower end portions of the front fork, a rear arm pivotally supported by a pivot support shaft at a rear portion of the body frame so as to be swingable up and down, a rear wheel supported at a swinging end of the rear arm, and dampers included inside the front fork and disposed so as to bridge the body frame and the rear arm.
The body frame is disposed with a head pipe that configures the front end portion of the body frame and supports the front fork, a frame body that extends rearward and downward from the head pipe and supports the rear arm at extension portions of the frame body, a seat bracket that extends rearward from the frame body and supports a seat, and an internal combustion engine that is supported at the frame body and is interlocked and coupled with the rear wheel. The body frame is supported on a traveling road surface by the front and rear wheels.
At the time the vehicle is traveling due to driving of the internal combustion engine, an impact force is applied to the body frame from the traveling road surface via the front and rear wheels, regardless of the presence of the dampers. Here, because it is difficult for the impact force applied to the body frame from the traveling road surface to be damped by the body frame itself when the rigidity of the body frame is too high, the vehicle tends to travel while bouncing from the traveling road surface each time the impact force is applied to the body frame. However, this action of the vehicle is not preferable in terms of the steering stability.
Thus, the body frame is usually made elastically deformable to a certain extent, whereby the impact force is damped so that steering stability is satisfactorily maintained when the impact force is applied to the body frame.
Incidentally, because the vehicle is of a saddle-type, the constituent parts of the vehicle are disposed compactly to make the vehicle smaller in terms of the function of the vehicle, and there is a demand to make the vehicle lighter. For this reason, it is not easy to ensure sufficient strength and rigidity for the portions of the body frame. For instance, when the vehicle is used for racing and a large impact force (kickback) is instantaneously applied to the body frame during high-speed travel, there is the potential for elastic deformation of the body frame to become large, and this large deformed state tends to persist, which also hinders steering stability and is not preferable.
Also, the cross section of the rear arm is made into a box-like shape and an interior space thereof is filled with polyurethane foam, whereby high rigidity is secured for the rear arm of the vehicle body and vibrational sound is reduced.
Incidentally, because the foam has compression strength, in a case where the rear arm is elastically deformed by an impact force, it is conceivable for the foam to work, with respect to elastic deformation in which the cross-sectional area of the rear arm is compressed, to counter this compression so that the elastic deformation is suppressed and satisfactory steering stability is maintained. However, because the foam does not include tensile strength, it is difficult for the foam to work against elastic deformation in which the cross-sectional area of the rear arm expands, so that this elastic deformation cannot be sufficiently suppressed. Thus, the above-described configuration is insufficient in terms of maintaining satisfactory steering stability by suppressing elastic deformation of the body frame resulting from the impact force.
Moreover, in terms of the properties of the foam, it is also conceivable for the working of the foam in terms of strength to be insufficient simply by applying the foam to outer surface sides of the body frame. Thus, the cross section of the body frame is made into the box-like shape and the interior space of the rear arm is filled with the foam. However, when the foam is disposed in this manner, a constraint is placed on the cross-sectional shape of the body frame and molding of the body frame tends to become cumbersome.
The present invention was devised in light of the above-described circumstances, and it is an advantage thereof to ensure that, in a case where an impact force applied to a body frame from a traveling road surface during travel of a vehicle is to be damped by elastic deformation of the body frame, the body frame is deterred from greatly elastically deforming so that the steering stability can be satisfactorily maintained when a large impact force is applied to the body frame. It is also an advantage of the invention to ensure that molding of the body frame can be achieved easily, even in such a case.